Dieting shouldn't be a chore. Eating healthy is a mindset, vacation or otherwise. Once you start getting into the groove of things and incorporating different food groups in your meal, it becomes (as someone already mentioned) a lifestyle. You can indulge, but it doesn't mean you have to neglect eating a healthy diet along the way.
For the last month, I've been on vacation. While in Thailand, I found myself eating a lot, but it doesn't mean eating a lot of bad foods. Because I had habits of eating my green, fruits and lean meat, I didn't have to think twice about passing up the deep fried sea food when I know I can get better quality, leaner, healthier option for about the same price.
I'm a foodie and I'd rather savour the very delicious cuisines available while on vacation knowing I'm eating local fresh produce and ingredients, than eating anything I could get in fast food restaurants or cheescake factories
When it comes down to performance eating, definitely grab tins of tuna. Oats or cereal should be enough for breakfast. I also bring some almonds and dark chocolate whenever I need some sweet cravings.